This invention relates to an improved keyboard mechanism for a single element typewriter or printer, and more particularly to a keylever signal storage mechanism for storing and typing the character according to a key which is depressed prior to the completion of a printing cycle of a previously depressed key.
A single element typewriter or printer has been already proposed wherein a keyboard generates coded electric signals for controlling an electromechanical character selection apparatus to select a character on the single print element in accordance therewith, and conventionally, a cyclically operable drive means is rendered operative in response to depression of a key to activate such electromechanical character selection apparatus as well as a printing means for actuating the print element to impact the selected character against the typewriter platen. In such typewriters, a key operable interposer is conventionally unlatched upon depression of a key to move from a normal position of rest to an operative position. Coding means is actuated to generate coded electric signals and then the cyclically operable drive means initiates its power driven operations, whereafter the interposer is restored to the normal rest position by a suitable restoring means driven by the drive means. Such sequence of operations is thus significantly different from that of a conventional single element typewriter such as disclosed in, for example, U.S. Pat. No. 2,919,002.
In order to obtain a high average typing speed, a single element typewriter or printer is conventionally provided with a mechanical storage means whereby a key signal after a preceding key has been depressed is stored until the preceding print cycle has been completed, then the stored signal automatically initiates another print cycle. Various proposals have been made to provide such mechanical storage means, but due to sequential differences of operations, only a few of them are applicable to a single element typewriter which has coding means and electromechanical character selection means as mentioned above.
U.S. Pat. No. 3,721,327 discloses a suitable keylever signal storage means applicable to such typewriters which includes, in addition to a first locking means to permit only one first interposer at a time to move to its actuated operative position, a second locking means to permit only one second interposer at a time to move to its operative position and to hold another subsequently released second interposer in an intermediate stored position. In response to restoration of a second interposer from the operative to the normal position towards the end of the print cycle the subsequently released second interposer is moved from the intermediate stored to the operative position thereby initiating another print cycle. The disclosed storage means, however, is disadvantageous in that a second depression of a key during the print cycle initiated by a first depression of the key may be ignored by the machine because of a sequence of machine operations in which the second interposer and accordingly the first interposer are not restored to their respective normal positions till the end of the print cycle. Such sequence of operations is inevitable due to the constitution of the storage means that engagement of a second interposer with the second locking means enables the latter to hold another subsequently released second interposer to the intermediate stored position.
Moreover, according to the disclosed storage means, there must necessarily be a complicated vertical and horizontal interconnection between a first interposer and a corresponding second interposer. Such interconnection means that downward movement of the first interposer to the actuated position depresses and releases the second interposer from latch means thereby permitting same to be moved by a spring in a horizontal direction to the operative position and into engagement with the second locking means. Upon such movement of the second interposer to the operative position, the first interposer is moved thereby in the horizontal direction out of engagement with the first locking means while it is held in the actuated position and in engagement with the first locking means by the second interposer in the intermediate stored position.
Such complicated interconnection is established by interchanging lugs formed on the first and second interposers and is disadvantageous in that it requires strict accuracy of parts and assemblage or otherwise the signal storing feature will be damaged. For example, a first interposer is disengaged from the first interlocking means by a corresponding second interposer in the intermediate stored position thereby permitting another first interposer to be moved to the actuated position. Another corresponding second interposer is permitted to move to the intermediate stored position whereby any number of second interposers may be brought to the intermediate stored position.